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Possible causes for Stuttering, Juddering and Stalling playback [2010-11-23]


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#1 boots2x

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Posted 23 November 2010 - 05:32 AM

We've been tracking a number of issues that can and do cause un-even playback. There are several different types of 'stuttering' playback. This post is a collection of trouble-shooting steps that you should take when trying to work out why you might be seeing 'stutter' playback.

Step 1 - Check this post and make sure you have the latest version of Plex and any Hot-fixes installed.

Step 2 - Check this list for the best description of your problem.

A/V sync
When the audio track and video track are not matching up, resulting in (most noticeable) mouths moving and the dialog not matching the facial movements.

Judder
When a television doesn't refresh quickly enough or doesn't stitch frames properly resulting in a "hopping" motion when panning left to right or experiencing fast motion. Judder is almost always at perfectly regular intervals, its not a random stutter, but rather a regular skip every x seconds or whatever, in medium to high motion scenes.

Stuttering
When audio continues, but frames are dropped, resulting in a pause, then a speed up of frame rate to catch up to the audio track. Stutter can be caused by CPU starvation - which can be more subtle. You may see dropped frames in the 'Info' overlay when playing video. To drop down the overlay, press 'i' whilst playing a video.

Stalling
When your network cannot keep up with the video file and the playback stops all together, then rebuffers to proceed. This results in a total pause of video/audio playback, then resuming.


Step 3 - Check through the list of possible causes for your problem. We recommend you check each of the items, even if you're 100% sure that "this is not the cause of the problem". The exception to this is when faced with a Mac OS X downgrade as that is a certified Pain in the Behind.

Stutter
Recap - Stutter playback is a non-regular pause in playback - like your Mac is running out of steam, then catches up. If you're seing a regular pause, check the 'Judder' section.

Other Applications Running
Playing HD media is demanding of your computer's resources. Make sure Plex and the Plex Media Server are the only applications running - and we really mean, No Other Apps/Utilities/Widgets Running. A good way of checking this is to open the Activity Monitor and look for any applications that are using CPU cycles or driving disk activity. You may have installed a background app that is eating away at your system's resources.

Mac OS X Preferences
Desktop Picture Changing can cause periodic stuttering when the picture change is occurring. Disable this option. Mac OS X Preferences > Desktop & Screensaver > Desktop > deselect, 'Change Picture'

Plex Media Server Scanning frequency
Plex Media Server will periodically scan your library for new and changed media. This scan can tax both CPU and Hard Drive. Either set scanning to 'Manual' or daily:

  • Click the PMS icon '>' in your Mac's menu bar, choose Preferences
  • Choose Library
  • Deselect "Update my library when changes to my folders are detected"
  • Select "daily" or Deselect "Update my library" to update the library manually. Manual update is done by Plex '>' icon > Update Library

DTS-HD or MA, Dolby Digital TrueHD Audio Tracks
These tracks will cause stuttering playback. There is currently no work-around this other than to re-encode the tracks to standard DTS/AC3.

H.264 Hardware Acceleration
Some users - particularly with Mac Mini 2009/2010 models - have reported stuttering playback with H.264 coded media and Hardware Acceleration enabled in the Plex Client. Some users have also reported issues with Mac OS X 10.6.4 and Hardware Acceleration. To check this possibility:

  • Disable H.264 Hardware Acceleration in the Plex Client. Plex > Preferences > Video > Player > disable H.264 Hardware Acceleration and test playback
If playback is good with H.264 acceleration disabled and you really want to try enabling H.264 Hardware Acceleration:

  • Upgrade to Mac OS X 10.6.5, enable H.264 Acceleration and test playback. If playback is good, you're done.
  • If playback is still stuttering, downgrade your Mac to Mac OS X 10.6.3 and test playback again.
  • If playback is still stuttering, disable H.264 Hardware Acceleration and continue with other options here.

Alternate skin selected for the Plex Client
It has recently been identified that using Plex Client skins with animations such as 'Rotating Backgrounds' can cause a periodic stutter. If you're seeing a stutter every (say) 15-20 minutes, and are using a skin other than the default MediaStream skin, try switching back to the MediaStream skin and test playback


Judder
Recap - Judder is pauses in playback that are regular and consistent. Judder is fundamentally due to a mis-match between the media being played and the frequency the TV is set to.

Judder is a relatively easy issue to identify but not so easy to eliminate. There is a long technical explanation for judder which will be covered in the Wiki shortly. The quick explanation is that a movie file coded at 24fps best played on a TV set to 24 or 120Hz. If not, the mis-match between the movie's fps and the TV's refresh will cause Judder. It will be regular - and depending on the mis-match either very subtle or quite jarring. To identify this issue:

  • Find a movie that shows judder
  • Analyze it in MediaInfo
  • Identify the fps
  • Set your TV to the same or as close to the same or multiple of the fps. For example, a 25fps film will play best on a TV set to 50 or 100Hz
  • Play with the settings available in the Mac OS X Display preferences for your TV
Here is a table that will help:

fps:Hz.jpg

Often, TV's will feature 'Motion Smoothing' features that 'help' with some media playback. These features add complexity when trouble-shooting issues and are best disabled. If your TV has these features, please disable them whilst diagnosing playback issues.

A/V Sync
Coming Soon

Stalling
Coming Soon

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Check the Plex Media Preparation Guide! | Learn how to collect Log filesGet MediaInfo to analyse video files

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#2 Fauzi

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Posted 29 November 2010 - 06:23 AM

Boots,

Great consolidation, man...

One quick question... In the DTS-HD, etc section, you say to re-encode the tracks... How?

I got as far as extracting the tracks from the mkv file using MKVExtract... Then what? How do I re-encode?

-Fauzi

#3 Prince

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Posted 28 January 2011 - 12:23 AM

Hi!

I have the "judder" issue when using Plex on my Mac Mini (2,26 GHz C2D) to play movies on my new Samsung UE55C8705.

After reading your excellent post I took Avatar 1080p Blu-Ray and identified it as 24 fps. I then changed the video output on the Mac Mini to 1080p/24hz. This actually solved the judder, but instead the audio got way out of sync.

What to do next?

#4 Just1n

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Posted 28 January 2011 - 02:51 AM

Hi!

I have the "judder" issue when using Plex on my Mac Mini (2,26 GHz C2D) to play movies on my new Samsung UE55C8705.

After reading your excellent post I took Avatar 1080p Blu-Ray and identified it as 24 fps. I then changed the video output on the Mac Mini to 1080p/24hz. This actually solved the judder, but instead the audio got way out of sync.

What to do next?


try turning off hardware decoding

#5 MikeyF

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Posted 28 January 2011 - 07:46 AM

Great Information - thank's!


Just one short question - If I play a movie with 25fps and the display setting is at 50Hz - who converts 25fps to 50fps? Plex? MacOSX? the TV Set?


greetings
michael

#6 Prince

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Posted 28 January 2011 - 08:21 AM

try turning off hardware decoding


Thanks! This made the A/V sync problem better, but not perfect. Is there anything else to try?

#7 Chris C

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Posted 28 January 2011 - 08:29 AM

Just one short question - If I play a movie with 25fps and the display setting is at 50Hz - who converts 25fps to 50fps? Plex? MacOSX? the TV Set?

It depends on your settings. If the computer is set to output at 50Hz, then it will be taking the 25fps video and basically just send showing a single frame for 2 refreshes, thus getting through all 25 frames after exactly 50 refreshes (and, thus, one second).

If you somehow have, say, the computer set to output at 50Hz, but the TV is displaying at 60Hz (I'm not aware of this actually being possible, but I suppose it might be for some TV sets), then the TV is going to have to do some really weird frame conversions to get the 50Hz signal displayed at 60Hz.

The most common kind of conversion most people would encounter is known as "3:2 pulldown" (or 2:3 pulldown) and converts 24fps to 30fps (for display at 60 or 120Hz). You can find some information about conversions here or here.

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#8 MikeyF

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Posted 31 January 2011 - 05:30 AM

It depends on your settings. If the computer is set to output at 50Hz, then it will be taking the 25fps video and basically just send showing a single frame for 2 refreshes, thus getting through all 25 frames after exactly 50 refreshes (and, thus, one second).

...

The most common kind of conversion most people would encounter is known as "3:2 pulldown" (or 2:3 pulldown) and converts 24fps to 30fps (for display at 60 or 120Hz). You can find some information about conversions here or here.


Hi!

Thanks for the information. Great second link (dvdfile.com) - another - "Thank You"!


If I understood everything correct, even on a PAL DVD the movie is stored with 24fps. The DVD Player (in our case - the Plex Player) converts it to 25 fps (If the MAC Display is set to 50Hz) or 30fps (It the MAC Display is set to 60Hz). Correct?

So when watching a PAL DVD on a PAL TV Set (50Hz) with Plex and the Mac Display Refresh Rate is set to 50Hz nothing can go wrong, correct?

So if I still have problems with stuttering pan shots - I have to find the solution somewhere else. It is not the framerate or the framerate conversion, correct?


greetings
Michael

#9 xbenderCH

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Posted 06 February 2011 - 07:52 AM

Thank you for the great info and the clearification of Judder, Stalling & Stuttering!

On my Plex/Nine installation, I always run into Stalling & Stuttering with some m2ts files. As an example: The issues always happen on the LIONSGATE intro sequence.

The same files play withouth any issues at all on VLC or XBMC :(

But of course, I like PLEX much more and especially the media server.

btw: I use the latest OS/X Snow Leopard on my Mac Mini (and downgrading is not an option) and after some other unsuccessful tries, I completely reinstalled PLEX... but still having the same issues :(

Any advice?
Best,
xbenderCH

#10 abmedic

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Posted 14 February 2011 - 04:12 PM

boots2x (and others): Thank you for the excellent consolidation and troubleshooting info on some playback issues. Rookies like myself would be lost without the suggestions and troubleshooting provided.

My issues is stalling. My setup is a January 2010 version MacMini, running latest Mac OS-X 10.6 (all updates), 4GB RAM, 320GB HD, streaming movies over PowerLine adapter (200mbps) from D-Link 323 NAS. Plex version 0.85. Using Harmony One remote that functions flawlessly. I've never had issues before, with previously stellar playback to both my Plex machine and to a classic Xbox running XBMC (Plex MacMini on main TV; Xbox/XBMC on basement TV, also streaming from same NAS server via PowerLine).

The Stalling problem is: over the past 2 or 3 weeks, videos in .mkv format have begun to more frequently stall, where playback will initiate, then "Pause" repeatedly (stalls completely, no audio or video), presumably while Plex re-buffers, and then continue playback. The pausing/stalling happens fairly frequently (about every 5-10 minutes), but when playback continues the video and sound are both fine. I haven't had it happen yet with .m4v, .avi, or .mp4, strictly with .mkv files (usually about max 1.4GB file size). All media is stored on the NAS, and served via PowerLine to the Plex system. I tried disabling and then reenabling H.264 hardware acceleration, tried changing cache size from 5 seconds, to 7 seconds, to 20 seconds, back to 5 seconds, without apparently resolution. Increasing cache to 20 seconds, did result in fewer pausing/stalling breaks in .mkv video playback, but didn't entirely resolve the issue (i.e. happened 3 or 4 times in a 28 minute TV episode .mkv, versus 6 or 7 times when cache at 5 seconds). I ran the Mac's maintenance utilities via the terminal command (daily, weekly and monthly maintenance), rebooted system, restarted Plex, and continued to play with cache and H.264 settings as above, without resolution. The key thing is, prior to the past 3 weeks, I never had the problem -- .mkv files played fine (files that played fine multiple times previously when I watched them before, now stall/pause).

I haven't yet tried streaming videos using VLC, mostly because I've never done it before and not sure of how to use VLC to stream. All videos play fine if copied to the local hard drive, and played using VLC. I'm open to upgrading to Plex 9, but had been avoiding it due to time issues, the fact that Plex 8 was working perfectly for me, and not wanting to have to rescan media sources (about 2TB total of movies/TV shows on NAS drives).

Any suggestions? All help or general thoughts on the issue are great appreciated!

MacMini 2013 2.6GHz i7 8GB 1TB Fusion / Synology DS1511 3TB x 5 SHR / Universal Remote MX-780 / Yamaha RXV665


#11 Chris C

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Posted 14 February 2011 - 04:29 PM

@abmedic
(Just to be clear, this is the Plex/Nine forums. I haven't messed with Plex/Eight in quite a while, so my memory on details is fuzzy.)

Frankly, what you've described sounds like a network issue: it appears that Plex isn't receiving the content fast enough to be able to play uninterrupted. If you play a video in Plex and hit the "i" key to bring up play info, you should see some info on the "AQ" and "VQ", which are the audio and video queues (i.e. buffers). If either of them reach zero then Plex will have to rebuffer; VQ typically stays at 99% for me when watching content.

You can also test a file stored locally by right-clicking it in Finder and Open Using > Plex. My guess is that a local file will play perfectly in your Plex without any buffering issues.

It's possible that something's changed in your setup in the last few weeks that could cause changed network performance. Using a Powerline adapter also introduces additional possibilities (beyond a standard ethernet/gigabit network setup), such as some sort of interference in the electric lines themselves.

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#12 pmjb

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Posted 05 March 2011 - 12:37 AM

For me the issue with Plex .9 was buffering (Was buffering :) )

My setup:

1x2.4 GHz (intel core duo 2) Imac with 4gb of ram, 2x750 gb ministacks + time machine ministack daisy chained to each other and connected to Imac by firewire (this Imac is now my plex server); 1x macmini 1.8gHz (intel core duo 2), 4 gb ram; 1x macmini 2.0gHz (intel core duo 2), 4 gb ram. Both the macminis are attached to 40 inch LCDs and have eyeTV + ministack eyeTV archives and time machine ministacks attached via firewire. NAS backups of ministacks. All movies are mixtures of mp4, avi, mkv's.

All macs 10.6.6 with all updates, Plex Version 0.9.1.13-a1a039b on server + clients

Network Specs: gigabit switch + Cat5e cabling (edited - see below) throughout the house, the network and computer specs (imac is minimum) meet Plex requirements + NAS backups of ministacks.

I went from the content being attached to a macmini by the TV/LCD upstairs to being attached to an Imac downstairs and streaming across my home network from Imac downstairs (Plex server) to macminis throughout the house upstairs (clients). My principle issue was a progressively worsening buffering issues. It started as minor pausing on a regular basis through occasional movies, to being every movie and TV show with Paused on screen with buffering appearing on the paused screen................very frustrating and as I am not an expert by any means with computers and networks I was considering maybe having to change back to my original setup.

I had read that if you mount the drives on the network this could improve throughput across the network. But I was unsure where they were to be mounted, at the server or through each of the macminis or all of them............so tried all, combinations, but nothing appeared to be working, until I mounted the folders containing the media (on the imac) from the macminis........................this solved it!!!!!!!........no buffering smooth as silk.............now please understand I post this only as a means of saying what worked for me. Some maybe saying well.......idiot!!!!Of course that works. But like I said I am no expert on macs, home networks , etc, far from it.............

When I say I mounted the folders directly from the macminis I went into Finder, under the 'Go' tab, 'connect to server' (click on this). A dialogue/drop-down box appears you can either add the server directly with the plus sign or use the button next to it that (rectangular button with a clock on it?) - this provides a list of recent servers, select the computer that is your plex server, press connect, then a list of stuff will appear. This is where I made my mistake. I selected the ministacks............this didn't work (for me). However, when I selected the movies folder directly and saw that was mounted under network - no more buffering. I then did this for all the the other media - TV Shows, Music Videos, TopGear videos, etc (these were my media folders on the plex server attached on the firewire ministacks). I did this on both the macminis/clients. Problem solved (for me) no buffering...............

I hope this helps/is useful/or disregard if useless...........


pmjb :)

#13 boots2x

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Posted 05 March 2011 - 03:06 AM

For me the issue with Plex .9 was buffering (Was buffering :) )

I hope this helps/is useful/or disregard if useless...........

Thanks for sharing your experience!

James

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#14 Chris C

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Posted 05 March 2011 - 04:01 AM

Network Specs: gigabit switch + Cat 5 cabling throughout the house

I hope you actually mean Cat5e rather than regular Cat5. Straight Cat5 is meant for 10/100Mbps networking, not gigabit. Cat5e (or better yet Cat6) support actual gigabit networking. You can read about the differences. Depending on the network path being taken for data and the bitrate of the content in question, it's possible this could be one thing affecting your performance (again, assuming you actually mean straight Cat5).

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#15 pmjb

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Posted 05 March 2011 - 05:08 AM

Yep, sorry Cat5e......(Edited see above)

pmjb

#16 Hebhansen

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Posted 07 March 2011 - 08:03 PM

Great post - Really!
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#17 Colour Of Sound

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Posted 14 March 2011 - 06:25 PM

Does anyone know if the team are planning on implementing automatic refresh rate and/or resolution switching in an upcoming release? This would be a pretty epic feature, especially seeing as Boxee and XBMC don't have it for their Mac clients.

I imagine its difficult to implement for an Apple-related reason, but emulators like Genesis Plus and Boycott Advance have an automatic refresh rate and resolution switcher built in, that works really well when launching a game. It only switches the TV to VGA resolution of course, but it seems like there is hope that it can be implemented at higher resolutions.

This is my most wanted request, and is the feature I miss the most since moving over from XBMC on Linux (which was too damn labour intensive to get right - it may have done auto-switching, but I had to wade though lines of code to get there!)

If any of the devs can shine a light on this it would be great. All other refresh rate and resolution themed topics in the forums are gathering dust and haven't been updated for a while, but seeing as this is stickied it seems like a good place to ask.

Thanks!
C

#18 AK-47

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Posted 16 March 2011 - 02:01 AM

I've got the Mid-2010 Mac Mini with 4gb of ram and a 2TB external drive connected via USB 2.0. I started ripping my blu rays today starting with Episode 1 of Lost. It created a 7.5GB MKV file. Immediately as the Lost title comes up the audio goes in and out and the video starts to lag badly. I've checked the above steps and still no help. Any ideas?
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#19 Hebhansen

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Posted 16 March 2011 - 07:09 AM

I've got the Mid-2010 Mac Mini with 4gb of ram and a 2TB external drive connected via USB 2.0. I started ripping my blu rays today starting with Episode 1 of Lost. It created a 7.5GB MKV file. Immediately as the Lost title comes up the audio goes in and out and the video starts to lag badly. I've checked the above steps and still no help. Any ideas?



In Settings > Video

- Is h.264 deblocking disabled?
- is h.264 Hardware Decoding disabled?

If not try to disable, also disable high quality upscale
HB

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#20 AK-47

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Posted 16 March 2011 - 12:37 PM

In Settings > Video

- Is h.264 deblocking disabled?
- is h.264 Hardware Decoding disabled?

If not try to disable, also disable high quality upscale



I disabled all H.264 settings listed at the top of this topic in Preferences - Video - Players

I am at work right now but I'll look at the setting for high quality upscale when I get home. Thanks!
Mid-2010 2.4GHz Mac Mini - 2TB WD USB2.0 External Storage - Panasonic Viera TCP42G10 Plasma - Onkyo TX-SR605 7.1 Receiver




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